This invention relates to a form for supporting a building element relative to an underlying surface of soil material on which the element is to be mounted.
One type of construction of building includes the laying of a building element onto a ground surface with the building element being held in place so that it is at a fixed location. On top of the building element is then constructed the remainder of the building structure so that structure itself is also fixed in place and prevented from movement relative to other parts of the building.
In particular, but not exclusively, the building element is in the form of a cast concrete beam or slab which is laid upon supporting foundations, which may be piles but engages the surface of the ground or soil material forming the ground in between the foundations. The foundations act to hold the building element slab or grade beam in place. In many cases the grade beam or slab is cast in place by the formation of shuttering at the piles and extending across the piles following which the concrete is poured into the shuttering to form the grade beam or slab to a required height above the ground surface.
As is well known after the building is completed the soil material can swell due to the action of moisture or frost. At the sides of the grade beam, the soil movement simply causes sliding action of the soil past the grade beam with little tendancy to lift or heave the grade beam from its fixed position. However on the underside of the grade beam the soil material if it is forced upwardly with sufficient force can engage the grade beam sufficiently to cause heaving or lifting of the grade beam with consequential significant damage to the building structure or can cause cracking of a slab.
Three systems are currently available to resolve this problem and are relatively widely used in building systems of this type.
In the first system, the shuttering forming the grade beam is modified to include a horizontal panel above the ground surface so as to define a void between the underside of the completed grade and the upper surface of the soil. This void then allows the expansion of the soil material to occur without the soil material engaging the underside of the grade beam at all. This system is disadvantagous in that the initial shuttering or form work necessary for manufacture of the void is significantly more complicated than the conventional simple vertical panels and hence it is relatively expensive in labor costs. Furthermore the void can become filled with soil during the backfilling process thus losing the space between the underside of the grade beam and the upper surface of the soil and allowing the expansion to be transmitted from the soil to the grade beam to cause heaving.
In a second system, a rectangular body is laid on the soil surface prior to the location of the grade beam or the casting of the grade beam in place. One type of body for this system is manufactured from vertically extending cardboard sheets which are corrugated to provide sufficient strength in the vertical orientation during the initial casting or locating process but subsequently collapse under the increased load generated during the expansion process. This product is probably the most widely used product of this type but is unsatisfactory for a number of reasons. The main reason is that it tends to become weakened if wetted during the concrete casting process and can therefore collapse prematurely.
A third system provides a similar type of body which is located in place to provide the void and this product is made of organic material which is intended to decompose under the action of an applied enzyme. This product is unsatisfactory because it may fail by the fact that the decomposition may be too slow or inadequate and hence can transmit the compressive loads to cause the heaving of the grade beam.
Furthermore attempts have been made to replace the above products by a very light density foam material which is simply cut into a solid block of the foam of the required dimensions and is located in place under the grade beam as it is cast. This product is unsatisfactory in that the amount of displacement of the product is substantially directly proportional to the load applied so that there is some distortion during the initial loading during the casting of the beam and then as the loads increase during the expansion mode there is insufficient collapse to prevent transmission of the loads to the lifting of the beam. This product has therefore basically been rejected because the foamed material cannot provide the necessary parameters for compression of the product.
Up till now, therefore, there has been only relatively unsatisfactory solutions to this problem and while these solutions are widely in use, they certainly leave significant room for improvement if a product can be found therefore which provides the required collapse characteristics.